What Keeps the Lights On? BY AMY SPIVEY, PROFESSOR OF PHYSICS
“Our electrical power is so reliable that we forget to think about where it comes from.”
When was the last time you recall being somewhere when the power went out? Were you at home? Or on campus? It doesn’t happen very often, right? We are fortunate to live in a part of the world where homes and businesses have electricity close to 100% of the time. Our electrical power is so reliable that we forget to think about where it comes from. In fact, electrical power generation is complicated and constantly evolving, and it’s worth considering both how our electricity is generated and the scientific innovations involved in the process. Figure 1 shows the percentage of electrical power in the U.S. generated by utilities using different energy sources (1). Nationwide, we get about 61% of our electricity from fossil fuels (coal, natural gas, and petroleum combined), 17% from renewables (solar, hydroelectric, and wind energy), and 20% from nuclear power, which is emissions-free but not technically renewable. The “Other” category in Figure 1 includes geothermal energy, wood and wood fuels, and other less-prevalent sources. Although Figure 1 shows the energy mix used in the entire U.S., there is wide variability in the sources used depending on geography and local resource availability. For example, in 2020 Hawaii generated 68% of its electrical power by burning imported petroleum, while in Iowa 57% of the electrical power was generated using wind turbines (1). Our local public utility, Tacoma Power, generated about 80% of its electricity in 2020 using four hydroelectric dams in western Washington, with the rest coming from nuclear power and wind (2). The energy sources used for electrical power generation are constantly evolving. Figure 2 shows the percentage of U.S. electricity generated nationwide using different sources over the past 20 years (1). While the fraction of electricity generated using nuclear or hydroelectric power has stayed relatively constant, Figure 2 shows that natural gas has gradually replaced much of the coal-fired electrical power generation. Much of this change has been driven by low-cost natural gas obtained through fracking, but it also may reflect efforts to lower CO₂ emissions. (For each kilowatt hour of electricity generated, burning natural gas releases about half as much CO₂ as burning coal (3).) Figure 2 also demonstrates that the fraction of U.S. electricity generated using wind or solar energy has been on the rise during this time.
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